Capillary electrochromatography of hydrophobic amines on continuous beds

The capillary electrochromatographic separation performance of hydrophobic amines and a related quaternary ammonium compound on continuous beds based on polymers of acrylamide has been studied. The chromatographic bed is poly merized in situ and the character of the polymers with regard to hydrophobi city and charge has been systematically changed by regulating its content o f isopropyl and sulfonate ligands, respectively. The best performance was o btained for columns with a molar ratio of 1.80 for the sulfonate and isopro pyl groups, and resulted in efficiencies up to 200 000 plates per meter. Th e effects on retention, resolution and elution order by ionic strength, pH, and content of acetonitrile in the mobile phase have been investigated. Th e quaternary ammonium compound was always the least retained irrespective o f pH. By increasing the pH, a reversal of the migration order between the t ertiary and secondary amine was obtained. The results indicate a complex mi gration/retention mechanism where ion-exchange, adsorption and electrophore tic mobilities play a role. The concentration limit of detection could be l owered from 1.3 mug/mL to 50 pg/mL by using a high content of 2-propanol (9 6%) in the sample compared to dissolving the analytes in the mobile phase.